Polyurethane foams having high resilience are typically produced from a polyether triol and an isocyanate. The polyether triols typically have a number average molecular weight from 4,500 to 6,000 and an average functionality of from 2.4 to 2.7 hydroxyl groups per molecule. Toluene diisocyanate, diphenyl methane diisocyanate, toluene diisocyanate/diphenyl methane diisocyanate mixtures, and modified toluene diisocyanate or diphenyl methane diisocyanate versions are used to produce foams with broad processing latitude. Isocyanate functionality is typically 2.0, and in most cases not higher than 2.3 isocyanate groups per molecule. The polyether triols form resilient foams when combined with isocyanates having from 2.0 to 2.3 isocyanate groups per molecule under conditions which promote foaming. However, polyethers degrade when exposed to ultraviolet light and polyesters degrade by hydrolysis under hot, humid conditions.
U.S. Pat. No. 4,939,184 described the production of polyurethane foams from polyisobutylene triols and diols which were prepared cationically. The polyisobutylenes are premixed with an isocyanate, namely an isocyanate which is a mixture of meta- and para- isomers of toluene diisocyanate having a functionality of 2.0. Then water was added as a blowing agent to form the polyurethane foam. Foams obtained were of low resilience and were useful in energy absorbing applications.
U.S. patent application Ser. No. 08/494,640, incorporated herein by reference, described a high resilience polyurethane foam produced from a polydiene diol. The foam's resiliency was achieved by adding an aromatic polyisocyanate having a functionality of from 2.5 to 3.0 isocyanate groups per molecule to assure adequate crosslinking. The polydiene diol foams produced showed excellent humid aging properties in comparison to conventional polyurethane foams.
U.S. patent application Ser. No. 08/724,940, incorporated herein by reference, described a high resilience, high tear resistance polyurethane foam produced from a polydiene diol. The foam's resiliency was achieved by selecting an appropriate amount of a aromatic polyisocyanate having a functionality of from 1.8 to 2.5 isocyanate groups per molecule to assure adequate crosslinking. The polydiene diol foams produced showed excellent tear resistance and were near white in color.
In some applications for the above described foams, the foams will be exposed to the weather. These foams will degrade under prolonged exposure to heat, humidity and sunlight. It is desirable to have a resilient, flexible, light-stable foam which can resist degradation under prolonged exposure to the weather.